The radiation readings inside unit 1′s containment were unexpectedly low. It would be impossible to have the bulk of the melted fuel inside unit 1′s containment with those low radiation levels.

Recent survey inside Unit 1 containment vessel (Source: Tepco)

[...]

Unit 1 [containment vessel] appeared very black and charred, with a light amount of steam and condensation

[...]

The charred appearance could be a sign of some sort of explosive event inside containment.

[...]

The hydrogen explosion of unit 1 could have occurred in locations beyond just the refueling floor. This would explain the charred appearance of the containment structure and possibly some of the damage found inside so far.

[...]

The radiation readings in containment, around the building and in the torus room taken together point to the east side torus room as the general location of the melted fuel. With this being the case, TEPCO’s decommissioning plan will need to be changed. It also causes more concerns about radiation and contaminated substance releases from the plant. What is unknown at this point is if the fuel could have traveled further down inside the torus room that only has 2.7 meters of concrete foundation, or further laterally through the wall or openings between the torus room and other interconnected rooms between the reactor building and the turbine building.

Watch the SimplyInfo team present at the University of Chicago here and here

They do even better than that, I actually tracked down the original article on SimplyInfo, where they postulate that the radiation must be at least 10 Tera-Sieverts: http://www.simplyinfo.org/?p=5576

I think that's bit on the high side!

To their credit they explain how they arrived at it, so it's not just totally pulled off… wherever. But their core assumption of "point source behind at least 2 meters of concrete" does not really hold here, at all. However, I suspect they did make a few conversion errors just from the magnitude of it.

Jaw-dropping numbers. Look at the gradient along the west side of the torus, 1 Sv to 100k Sv within a few feet. If these numbers are correct, then there might be corium under the torus that leaked through the pipe holes.

Yeah you'd think….who knows, none of us is even close to an expert, tho thanks to TEPCO we're getting closer every day!

I have to say I'm grateful to TEPCO for giving me an all-expenses-paid education about nuclear power….they've even given me free bits of radioactive materials to carry around inside my body. I owe them one, just don't know yet how to repay!

That's what I was thinking as well -can the units really be right? I mean how does anyone walk out by his own feet after measuring that?… Planning his own funeral I guess. Or then he's pulled out of there by a rope after his collapse… That's just too much, too much…

hahahaha.. oh the good news, from industry professionals.. ahh they make me feel so reassured.. such Intelligence..

"Tepco has recently released measurements that provide convincing evidence that virtually all of the corium in Fukushima Daiichi unit #1 remains safely stored inside an intact reactor pressure vessel. Despite all claims to the contrary, no substantial quantities of that material have melted through the pressure vessel to fall onto the concrete floor of the surrounding containment structure.

It has always seemed far fetched to me to think that material from a nuclear reactor that melted several hours after fission has stopped contains the power density necessary to melt through carbon steel pressure vessels that are 6-12 inches thick."

Consider the source.. Rod Adams

Rod Adams gained his nuclear knowledge as a submarine engineer officer and as the founder of a company that tried to develop a market for small, modular reactors from 1993-1999.

He may actually be well meaning. The smaller the reactor, the exponentially less radioactive. You could pick up the core with tongs in a small reactor and put it in a lead bucket if it went into meltdown wearing a papersuit. Or, in case of a melt-through, use a shovel. Fissioning on a small scale is not the same as fissioning on a large scale. Reactor size makes the fissioning exponential in orders of magnitude. That's one of it's peculiarities. But, the argument for larger, vastly more dangerous reactors was that they could be centralized and under the control of a corporation. The smaller reactors would require PUD's and such and that risked changing the whole political and power landscape of energy production and delivery.

Solar is facing the same battle. It's not the technology that slowed it down, it was the politics. Remember Reagan's first act as President was to have the solar panels that Jimmy Carter erected on top of the White House removed on his first day in office and outlined a US Manifest Destiny to remain reliant on oil and to gain oil through any means necessary. Users and PUD's can make solar, deliver it, and set the cost. That's a no-no in the field of energy production.

With that level of radiation..life expectancy is pretty short..nanoseconds. So the plan is from TEPCO on how to get the radiation level lowered? You know, so TEPCO can remove the fuel rods from Reactor 1…(sarcasm)..

How many workers have been working near this area of the reactor? Like the poor guy found dead in his truck at a lunch break? Or some of the other heart attack episodes??

Yes, it would be nice to see a reference for the claims in this article. "Inconceivable" is the word, most likely an unit confusion.
Though first of all, sievert is not a unit that should safely be used here, to know sieverts you'd need to know the exact isotopes involved and body-parts affected. I guess we can assume they're going with "the mix of isotopes normally present in nuclear reactors" and fudging the numbers, and thus we can accept the ball-park figures…

And so, the exposed core of Chernobyl reactor right after the accident was 300 Sieverts/hour. Typical PWR used fuel bundle after 10 years cooling is quoted as 270 Sv/h. Much more than 500 Sieverts/hour, and you're making things up. The highest dose rate measured in Reactor #2 was 72.9 Sv/h, which is consistent with what you'd expect with some water shielding. That said, a couple meters of water will pretty much block radiation even from freshly spent fuel bundles.

Also the 270Sv/h for spent PWR fuel (at 10 years!) is off Wikipedia, which is why I went with it, but I believe them to be off by factor of 1000 – the usual "reading mSv as Sv" bug. Under 300 mSv is the design criteria for nuclear fuel that aged, and CANDU reactors (for which a reference exists) is quoted 50Sv/h after just a year.
But the range <500Sv/h is still valid, at million Sv/h you're talking about sustained hot *fusion* reaction, and we as a species are yet to even figure how to make that happen
The more interesting stuff in this vein came from TEPCO's release of the isotope content in the water:
Iodine: Below the detection limit
Cesium 134: 1.9 x 10^4 Bq/cm3
Cesium 137: 3.5 x 10^4 Bq/cm3

So there's definitely SOMETHING in that there containment (About ten times higher activity and thus dose rate, and relatively lower Cesium 134 content) but a lot of things can affect that… And no word on uranium content, for example?

So I believe the people writing the article of the topic may have "simply" confused Bq/m^3 for Sieverts/h, as the reported Bq/m^3 are in similar range:
"From the water retaining in North-East corner (of the torus room), they measured 4.1E+10 Bq/m3 of Cs-134 and 7.4E+10 Bq/m3 of Cs-137."

De-referencing the exponent notation and m^3 gives actually 4.1 x 10^4 Bq/cm^3 and 7.4 x 10^4 Bq/cm^3 respectively; numbers that are 2.1 times that in the PCV.

It would benefit to know the exact flow of water in there, but based on this I don't think it's possible to say the corium is in the torus room – one would expect the contamination to be worse than 2X if the corium was just laying in there for better part of two years while PCV is getting flushed by cooling water. I feel thinking it knew to stop in the torus room is wistful thinking.

I agree there is a typo… The highest value I ever read on the Tepco red graphs we watched so often in the early months was approaching 500 Sieverts per hour. They stopped updating those values March 15, 2012 at which time the last readings of the reactor vessel radiation showed Unit 2 as the hottest at 13.1 Sv/hr:

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